How do PCB designers handle huge currents on a PCB while keeping the track’s size small?

• To make the thickness of the copper as thick as possible. Thicker copper will add capacity, even though it is more costly.
• Create a multi-layer trace. You can make the layers have the same trace under the premise of ensuring heat dissipation.
• Add another wire between the two points.
• If the PCB uses a solder mask, you can add pads on the traces.

More reading: LED PCB Design Guide: Challenges & Considerations